But this requires the manufacturer of the IoT device to provide a central service like Plex does. Maybe they can't afford it, or the device is expected to run

But this requires the manufacturer of the IoT device to provide a central service like Plex does. Maybe they can't afford it, or the device is expected to run for a very long time, like even after the manufacturer goes out of business. Or as some other commenters have said, it's a personal / hobby project and the "manufacturer" doesn't have the means nor the will to maintain some outside management server.